Electro-optical device and electronic apparatus

ABSTRACT

An electro-optical device includes an insulating substrate, a switching element, at least one PIN diode, and at least one reflector. The switching element includes a first polysilicon semiconductor layer formed on the insulating substrate, and a gate electrode formed between the insulating substrate and the first semiconductor layer. Each of the at least one PIN diode includes a second polysilicon semiconductor layer formed on the insulating substrate. The at least one reflector is formed in the same layer as the gate electrode and opposite the second semiconductor layer or layers of the at least one PIN diode.

This is a Divisional of U.S. patent application Ser. No. 11/708,534filed on Feb. 21, 2007, which is hereby incorporated by reference in itsentirety. This application claims priority to Japanese PatentApplication No. 2006-054425 filed Mar. 1, 2006, which is herebyincorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to electro-optical devices and electronicapparatuses suitable for display devices that control their displayluminances.

2. Related Art

A liquid crystal panel includes two substrates, such as glass substratesor quartz substrates, and liquid crystal filled therebetween. Thesubstrates are provided with electrodes, and image signals are suppliedto the electrodes. The optical characteristic of the liquid crystalbetween the electrodes of the substrates changes according to the imagesignals. That is to say, by applying voltages based on the image signalsto the liquid crystal between the electrodes of the substrates, thealignment of liquid crystal molecules is changed. Thus, the lighttransmittance in each pixel changes according to the image signals, andan image display according to the image signals is performed.

In order to perform a high-luminance display in such a liquid crystalpanel, in general, a backlight unit is provided at the back of a liquidcrystal panel. A backlight unit that improves its illuminationuniformity using a light guide plate has been developed. By illuminatinga display region of a liquid crystal panel with a backlight unit, adisplay on the display region can be observed with a sufficientluminance.

The viewability of display of a liquid crystal panel changes dependingon the ambient brightness. For example, when the ambient light isbright, the display is less viewable, and therefore the illumination ofthe display region needs to be brighter. Conversely, when the ambientlight is sufficiently dark, the display region need not be brighter thannecessary.

JP-A-2003-78838 discloses a technique to provide an easily viewabledisplay independently of the ambient brightness. In the technique, theambient light is detected, and the luminance of a backlight unit iscontrolled on the basis of the feedback information.

The apparatus of JP-A-2003-78838 uses a discrete component as a lightsensor for detecting the ambient light. Therefore, the light sensorneeds to be mounted on a flexible printed board. This increases theman-hour and the cost.

To solve this problem, a PIN diode light sensor can be formed on asubstrate constituting a display panel, such as a liquid crystal panel.In this case, the PIN diode is formed in the same layer as thesemiconductor layer in the display region.

The semiconductor layer in the display region is set to a comparativelysmall thickness in order to obtain desired transistor characteristics.However, in the case where the semiconductor layer in the PIN diodeforming region is thin, incident light passes through the semiconductorlayer, and photogenerated charges cannot be efficiently generated. Thatis to say, light is not efficiently incident on the intrinsic layer, anda sufficient light sensitivity cannot be obtained.

SUMMARY

An advantage of some aspects of the invention is that an electro-opticaldevice and an electronic apparatus according to the invention can have asufficient light sensitivity by enabling light to be efficientlyincident on the intrinsic layer.

According to an aspect of the invention, an electro-optical deviceincludes an insulating substrate, a switching element, at least one PINdiode, and at least one reflector. The switching element includes afirst polysilicon semiconductor layer formed on the insulatingsubstrate, and a gate electrode formed between the insulating substrateand the first semiconductor layer. Each of the at least one PIN diodeincludes a second polysilicon semiconductor layer formed on theinsulating substrate. The at least one reflector is formed in the samelayer as the gate electrode and opposite the second semiconductor layeror layers of the at least one PIN diode.

Due to this configuration, the insulating substrate is provided with abottom gate switching element formed by the first semiconductor layerand the gate electrode, which is formed between the insulating substrateand the first semiconductor layer. In addition, the insulating substrateis also provided with the at least one PIN diode, which receives lightincident via the light-receiving surface of the insulating substrate.Part of the light incident on the insulating substrate passes throughthe second semiconductor layer of the at least one PIN diode. Betweenthe insulating substrate and the second semiconductor layer, the atleast one reflector is provided so as to face the second semiconductorlayer. The light passing through the second semiconductor layer isreflected by the at least one reflector and reenters the secondsemiconductor layer. Thus, most of the light incident from thelight-receiving surface of the insulating substrate can be made incidenton the at least one PIN diode, and the ambient light can be detectedwith high sensitivity.

Each of the at least one reflector is preferably wider than the secondsemiconductor layer of the corresponding PIN diode so as to face theentire region of the second semiconductor layer of the corresponding PINdiode.

Due to this configuration, most of the light passing through the secondsemiconductor layer can be reflected so as to reenter the secondsemiconductor layer. In addition, since the at least one reflector facesthe entire region of the second semiconductor layer, that is to say,both the cathode and the anode, the at least one reflector can beprevented from affecting the characteristics of the at least one PINdiode.

It is preferable that the at least one PIN diode include a plurality ofPIN diodes arranged on the insulating substrate and that the at leastone reflector include a plurality of reflectors each provided oppositethe second semiconductor layer of the corresponding PIN diode.

Due to this configuration, the change in characteristics of each PINdiode due to the reflectors can be uniformized, and stablecharacteristics can be obtained.

Each of the at least one reflector is preferably connected to apredetermined fixed potential point.

Due to this configuration, the at least one reflector is out of thefloating status, and the at least one reflector can be prevented fromaffecting the characteristics of the at least one PIN diode.

The predetermined fixed potential point to which each of the at leastone reflector is connected is preferably the anode or the cathode of thecorresponding PIN diode.

In this case, the configuration is simple, and the at least onereflector can be brought to a fixed potential.

It is preferable that the electro-optical device further include anilluminating unit that irradiates the insulating substrate withilluminating light, and a shielding plate for blocking the light fromthe illuminating unit from being incident on the at least one PIN diode.

Due to this configuration, the light from the illuminating unit isblocked from entering the at least one PIN diode by the shielding plate.Thus, the ambient light can be accurately detected by the at least onePIN diode.

It is preferable that an electronic apparatus include theelectro-optical device according to the above aspect of the invention.

Due to this configuration, the ambient light can be detected with highsensitivity, and display can be optimized according to the illuminanceof the ambient light.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a sectional view of an electro-optical device according to afirst exemplary embodiment of the invention.

FIG. 2 is a plan view of the electro-optical device according to thefirst exemplary embodiment.

FIG. 3 schematically illustrates the sectional structure of a liquidcrystal panel employed as the electro-optical device of FIG. 2, theliquid crystal panel being contained in a case.

FIG. 4 schematically illustrates the two-dimensional pattern of adisplay panel employed as the electro-optical device of FIG. 2.

FIG. 5 is an equivalent circuit diagram showing the connection status ofthe PIN diodes 29 and 30.

FIG. 6 is a perspective view schematically showing the electro-opticaldevice according to a second exemplary embodiment of the invention.

FIG. 7 is a perspective view showing an example of an electronicapparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The exemplary embodiments of the invention will now be described indetail with reference to the drawings. FIG. 1 is a sectional view of anelectro-optical device according to a first exemplary embodiment of theinvention. FIG. 2 is a plan view of the electro-optical device accordingto the first exemplary embodiment. FIG. 3 schematically illustrates thesectional structure of a liquid crystal panel employed as theelectro-optical device of FIG. 2, the liquid crystal panel beingcontained in a case. FIG. 4 schematically illustrates thetwo-dimensional pattern of a display panel employed as theelectro-optical device of FIG. 2.

First Exemplary Embodiment

First, the overall structure of the electro-optical device according tothe first exemplary embodiment will be described with reference to FIGS.2 to 4.

In FIG. 2, the electro-optical device 11 includes a display panel 21including two substrates stuck together. In the case of FIG. 3, a liquidcrystal panel is employed as the display panel 21. In this case, theelectro-optical device 11 includes the display panel 21 and anilluminating unit 22. A self-luminous display panel can also be employedas the electro-optical device. In this case, no illuminating unit isnecessary.

As shown in FIG. 3, the display panel 21 includes a light-transmittingelement substrate 23, a light-transmitting opposing substrate 24, andliquid crystal 25 enclosed therebetween. The element substrate 23 andthe opposing substrate 24 facing each other are stuck together with asealing material (not shown). The display panel 21 includes, forexample, a plurality of scanning lines 33 extending in the horizontaldirection (see FIG. 4), a plurality of data lines 34 extending in thevertical direction (see FIG. 4). Pixels are formed at the intersectionsof the plurality of scanning lines 33 with the plurality of data lines34.

on the element substrate 23 are disposed pixel electrodes (ITO) 36 (seeFIG. 4). On the opposing substrate 24 is provided an opposing electrode(common electrode (ITO)) (not shown). On the pixel electrodes of theelement substrate 23 is provided a rubbed alignment film (not shown) incontact with the liquid crystal 25. On the other hand, on the opposingsubstrate 24 is also provided a rubbed alignment film (not shown) incontact with the liquid crystal 25. Each alignment film is a transparentorganic film, for example, a polyimide film. In addition, on theopposing substrate 24 is formed a shielding film (not shown) along thedata lines 34 and the scanning lines 33.

Although not shown in FIG. 3, the observing side of the opposingsubstrate 24 and the side opposite from the element forming surface(hereinafter also referred to as “light receiving surface”) of theelement substrate 23 are each provided with a polarizer. The polarizingaxes of these polarizers are set so as to correspond to the rubbingdirections of the alignment films formed on the element substrate 23 andthe opposing substrate 24.

The illuminating unit 22 functioning as a backlight unit emits lightfrom under the element substrate 23 of the display panel 21. Theilluminating unit 22 includes, for example, a plurality oflight-emitting diodes (hereinafter referred to as LEDs) serving as alight source, and a light guide plate. The light from the LEDs is guidedinto the light guide plate, is reflected and scattered by reflectinglayers on the bottom surface and the side surfaces of the light guideplate, and is then emitted from the upper surface of the light guideplate. In this way, backlight is incident on the display panel 21disposed above the illuminating unit 22.

The illuminating unit 22 and the display panel 21 are contained in acase 26, being stacked one on top of the other. The case 26 has anopening 27 formed in the upper surface thereof. The display panel 21 isfixed inside the case 26 so that a screen 13 of the display panel 21faces the opening 27.

The display panel 21 has an effective display region 14 in the center ofthe screen 13 defined by the opening 27 of the case 26. In the effectivedisplay region 14 are formed pixels corresponding to the intersectionsof the scanning lines 33 with the data lines 34.

In the display panel 21, the data lines 34 are supplied with imagesignals, and the scanning lines 33 are supplied with scanning signals.Thus, each pixel is driven on the basis of the image signals and changesits light transmittance. The light entering the display panel 21 fromthe illuminating unit 22 is modulated in the effective display region 14of the display panel 21. Therefore, when the effective display region 14is observed from the opening 27 side of the case 26, an image can beviewed. On the opposing substrate 24 is formed a shielding film 28 (theshaded area in FIG. 2) for shielding the periphery of the opposingsubstrate 24. The shape and the size of the effective display region 14are defined by this shielding film 28.

on the periphery of the effective display region 14 in the screen 13 isprovided a non-display region 15. In this non-display region 15 areprovided light-receiving-element disposing regions 16 and 17 fordisposing PIN diodes 29 and 30, respectively, which are light receivingelements for detecting the illuminance. In the light-receiving-elementdisposing region 17, the shielding layer 28 is formed on the opposingsubstrate 24 so as to block the ambient light from being incident on theelement substrate 23.

The light-receiving-element disposing region 16 is provided in anopening region 19 where the shielding film 28 is not formed on theopposing substrate 24. The light-receiving-element disposing region 16transmits light from the upper surface (observing surface) of theopposing substrate 24.

In the light-receiving-element disposing region 16 are disposed the PINdiodes 29. In the light-receiving-element disposing region 17 aredisposed the PIN diodes 30. The ambient light entering from theobserving surface of the opposing substrate 24 is incident on the PINdiodes 29, which can thereby detect the illuminance of the ambientlight. On the other hand, the ambient light is blocked from beingincident on the PIN diodes 30 by the shielding film 28. Therefore, thePIN diodes 30 can be used, for example, for detecting the dark current,or for detecting the backlight from the illuminating unit 22.

As shown in FIG. 4, the plurality of scanning lines 33 extend from a Ydriver 31, and the plurality of data lines 34 extend from an X driver32. At the intersections of the scanning lines 33 with the data lines 34are provided switching elements 35. The switching elements 35 are ON-OFFcontrolled by the scanning signals supplied from the Y driver 31 to thescanning lines 33. When turned on, the switching elements 35 supply theimage signals supplied from the X driver 32 to the data lines 34 to thepixel electrodes 36.

Although the display panel 21 shown in FIG. 4 is a TFT liquid crystalpanel, other active matrix display panels can also be employed as longas the pixels in the effective display region are driven by drivers.

A terminal portion 37 is provided on a short side of the display panel21 near which the X driver 32 is disposed. The Y driver 31 and the Xdriver 32 are connected to the terminal portion 37 by interconnects (notshown).

As shown in FIG. 4, the PIN diodes 29 are provided in thelight-receiving-element disposing region 16, and the PIN diodes 30 areprovided in the light-receiving-element disposing region 17. The PINdiodes 29 and 30 are formed by providing an I-type region between aP-type region and an N-type region. Although the I-type region means“intrinsic region,” the I-type region may be doped sufficiently morelightly than the N-type region or the P-type region.

As shown in FIG. 4, the cathodes of the PIN diodes 29 arecommon-connected and are connected to a terminal 41, and the anodes ofthe PIN diodes 29 are common-connected and are common-connected to thecathodes of the PIN diodes 30 and a terminal 42. The anodes of the PINdiodes 30 are common-connected and are connected to a terminal 43.

Each PIN diode 29 generates an output based on the illuminance ofincident light. Each PIN diode 30 generates an output based on the darkcurrent. This configuration makes it possible to remove the component ofthe dark current and to detect the illuminance of the ambient light.

FIG. 5 is an equivalent circuit diagram showing the connection status ofthe PIN diodes 29 and 30 in this case. The PIN diode 29 is used fordetecting the ambient light. The PIN diode 30 is used for detecting thedark current.

In the example of FIG. 5, the terminal 41 is connected to a powerterminal, and the terminal 43 is connected to a reference potentialpoint. The PIN diodes 29 and 30 are series-connected between the powerterminal and the reference potential point. A capacitor C11 is providedbetween the reference potential point and the terminal 42, which isconnected to the connection point between the PIN diodes 29 and 30. Theterminal 42 is also connected to an output terminal 46 via an amplifier45.

Due to this configuration, the diode 30 generates an output based on thedark current, and the diode 29 generates a detection currentcorresponding to the ambient light. Thus, a current that is thedifference between the dark current and the detection currentcorresponding to the ambient light flows into the amplifier 45 connectedto the connection point between the diodes 30 and 29. Thus, theamplifier 45 outputs a detection current of the ambient light from whichthe dark current component is removed.

In this exemplary embodiment, the switching elements 35 in the effectivedisplay region 14 and the PIN diodes 29 and 30 in thelight-receiving-element disposing regions 16 and 17 include polysiliconsemiconductor layers on the element substrate 23, which is an insulatingsubstrate. In this exemplary embodiment, bottom gate TFTs (thin filmtransistors) are employed as the switching elements 35 in the effectivedisplay region 14.

FIG. 1 shows an example of the sectional structure of the PIN diodes 29and 30. FIG. 1 is a sectional view taken along line I-I of FIG. 4.

In the display panel 21 of FIG. 1, a base insulating film 71 is formedon a transparent insulating substrate 23, such as a quartz substrate ora glass substrate.

First, the configuration of a region where pixels are formed will bedescribed, the region including the effective display region 14.

In the region where pixels are formed, gate electrodes 76 are formed onthe base insulating film 71. Each gate electrode 76 constitutes a TFTserving as a switching element. The gate electrodes 76 are formed of ametal material, for example, chromium, molybdenum, or titanium. The gateelectrodes 76 are connected to the scanning lines 33. On the baseinsulating film 71 and the gate electrodes 76 is formed an oxide film75.

On the oxide film 75 are formed semiconductor layers 73 eachconstituting a TFT. The semiconductor layers 73 are formed ofpolysilicon, which is a polycrystalline semiconductor. The polysiliconis formed by laser-annealing and crystallizing amorphous silicon, whichis a non-single-crystal non-crystalline semiconductor.

The both ends of each semiconductor layer 73 are doped so as to form asource region 72 and a drain region 74.

The source region 72 and the drain region 74 have an LDD structure. Thatis to say, the source region 72 and the drain region 74 have acomparatively lightly doped part near the channel region above the gateelectrode 76. In order to form an LDD structure in the semiconductorlayer 73, the semiconductor layer 73 is doped twice so as to form alightly doped region and a heavily doped region in the source region 72and the drain region 74. In the first doping process, the entire regionof the source region 72 and the drain region 74 is heavily doped. Next,after a channel protecting film 77 is formed on the semiconductor layer73, the second doping process is performed. In the second dopingprocess, both ends of the semiconductor layer 73 is comparativelylightly doped. At this time, the channel protecting film 77 is used as amask.

on the semiconductor layers 73 and the channel protecting films 77 isformed an interlayer insulating film 78. The interlayer insulating film78 has contact holes 78 a and 78 b formed over the source region 72 andthe drain region 74, respectively, of each TFT. The source regions 72are connected to the data lines 34 via the contact holes 78 a.

On an interconnect layer in which the data lines 34 are formed and onthe interlayer insulating film 78 is formed another interlayerinsulating film 79. The interlayer insulating film 79 has contact holes80 formed therein. The drain region 74 of each TFT is connected to thecorresponding pixel electrode 36, which is formed on the interlayerinsulating film 79, via the corresponding contact holes 78 b and 80.

In the light-receiving-element disposing regions 16 and 17, the PINdiodes 29 and 30 are formed on the base insulating film 71. The PINdiodes 29 and 30 are formed in the same manufacturing process as theTFTs in the effective display region 14.

That is to say, each PIN diode 29 has an N-type region 51, a P-typeregion 53, and an I-type region 52 in a semiconductor layer 49 formed inthe same layer as the semiconductor layers 73. The N-type region 51 isdoped with an N-type impurity. The P-type region 53 is doped with aP-type impurity. The I-type region 52 is an intrinsic semiconductor oris doped with a very small amount of impurity. Each PIN diode 30 has anN-type region 54, a P-type region 56, and an I-type region 55 in asemiconductor layer 50 formed in the same layer as the semiconductorlayers 73. The N-type region 54 is doped with an N-type impurity. TheP-type region 56 is doped with a P-type impurity. The I-type region 55is an intrinsic semiconductor or is doped with a very small amount ofimpurity.

These regions 51 to 56 are formed on the oxide film 75 which is the samefilm as that in the effective display region 14. On the channel of eachsemiconductor layer 49 is formed a channel protecting film 57. On thechannel of each semiconductor layer 50 is formed a channel protectingfilm 58. The channel protecting films 57 and 58 are formed in the sameprocess as the channel protecting films 77 of the TFTs and are, forexample, oxide silicon films.

As described above, in the effective display region 14, in order to forman LDD structure in each semiconductor layer 73, two doping processesare performed. The channel protecting films 57 and 58 can block theI-type regions 52 and 55 from being lightly doped in the second dopingprocess.

The interlayer insulating film 78 has contact holes 78 c to 78 f formedover the N-type region 51 and the P-type region 53 of each PIN diode 29and the N-type region 54 and the P-type region 56 of each PIN diode 30.On the interlayer insulating film 78 and in the same layer as the datalines 34 are formed interconnects that are connected to the terminals 41to 43. The regions 51, 53, 54, and 56 are connected to theseinterconnects via the contact holes 78 c to 78 f. The interconnects havea three-layer structure of, for example, titanium, aluminum, andtitanium. To the terminal 42 are common-connected the N-type regions 54and the P-type regions 53.

On the interconnect layer on the interlayer insulating film 78 and onthe interlayer insulating film 78 is formed the interlayer insulatingfilm 79. On the pixel electrodes 36 and the interlayer insulating film79 is formed an alignment film 84 in contact with the liquid crystal 25.The alignment film 84 is rubbed in a predetermined direction.

On the other hand, on the opposing substrate 24 is formed a shieldingfilm 28, which defines the effective display region 14 and the openingregion 19 (see FIG. 2). On the shielding film 28 and the opposingsubstrate 24 is formed a common electrode 85. On the common electrode 85is formed an alignment film 86. The alignment film 86 is rubbed in apredetermined direction. The observing side of the opposing substrate 24is provided with a polarizer 92.

In this exemplary embodiment, a reflector 59 is formed under each PINdiode 29 detecting the illuminance of the ambient light. Each reflector59 is formed in the same layer as the gate electrode 76 constitutingeach switching element in the effective display region 14. Eachreflector 59 is formed opposite the corresponding semiconductor layer 49with the oxide film 75 therebetween. Each reflector 59 reflects thelight entering from the opposing substrate 24 side, passing through thecorresponding semiconductor layer 49, and traveling toward the elementsubstrate 23 so that the light is incident on the corresponding I-typeregion 52.

Thus, most of the light incident via the opening region 19 can be madeincident on the I-type regions 52.

The illuminating unit 22 includes an outer frame 38 and a light guideplate 39 fitted in a depression in the outer frame 38. On the lightguide plate 39, at least in the effective display region 14, an opticalsheet 40 is disposed. The light from the light guide plate 39 isdiffused and emitted upward by the optical sheet 40. On the opticalsheet 40 is disposed a polarizer 91.

Opposite the light-receiving-element disposing regions 16 and 17, ashielding plate 18 is provided on the outer frame 38 and the light guideplate 39. The shielding plate 18 blocks light from the light guide plate39 from traveling toward the PIN diodes 29 and 30. Each reflector 59blocks the light from the illuminating unit 22 from traveling toward thecorresponding PIN diode 29.

Due to the above configuration, the light incident from the observingside of the opposing substrate 24 travels toward the element substrate23 via the opening region 19. Part of this incident light is incident onthe I-type region 52 of each PIN diode 29 from above. However, anotherpart of the incident light passes through each semiconductor layer 49and travels toward the element substrate 23. In this exemplaryembodiment, under each semiconductor layers 49, the reflector 59 isprovided. The ambient light passing through the semiconductor layers 49is reflected by the reflectors 59 disposed under the semiconductorlayers 49 and enters the I-type regions 52 of the PIN diodes 29 frombelow. Thus, a sufficient amount of ambient light can be made incidenton the I-type regions 52 of the PIN diodes 29.

In each PIN diode 29, a detection current corresponding to thephotogenerated charge flows via a depletion layer generated in theI-type region 57. This detection current is output to the outside viathe interconnects connected to the regions 51 and 53. Thus, theilluminance of the ambient light can be detected.

The ambient light is blocked from being incident on the PIN diodes 30 bythe shielding layer 28, and therefore the PIN diodes 30 can detect thedark current. The PIN diodes 29 can also detect the illuminance of thebacklight from the illuminating unit 22.

By using the detection results of the PIN diodes 29 and 30, for example,the brightness of the illuminating unit 22 can be controlled accordingto the brightness of the ambient light. For example, when the PIN diodes29 and 30 detect that the ambient light is bright, the brightness of theilluminating unit 22 is increased according to the brightness of theambient light. This can improve the visibility of display.

As described above, in this exemplary embodiment, the reflectors 59 areprovided under the PIN diodes 29, and the ambient light passing througheach semiconductor layer 49 can be made incident on the I-type region ofeach PIN diode 29. The reflectors 59 are formed in the same layer as thegate electrodes constituting the transistors in the pixel region, andcan therefore be formed without increasing the number of processes. Asdescribed above, in this exemplary embodiment, it is possible to make asufficient amount of ambient light incident on the light receivingdiodes and to ensure a detection of the illuminance of the ambientlight.

Second Exemplary Embodiment

FIG. 6 is a perspective view schematically showing the electro-opticaldevice according to a second exemplary embodiment of the invention. InFIG. 6, the same reference numerals will be used to designate the samecomponents as those in FIG. 1, so that the description will be omitted.

The reflectors 59 in the first exemplary embodiment are formed of metaland are in a floating status. Therefore, an unforeseen parasiticcapacity is generated between the cathode (N-type region 51) of each PINdiode 29 and the corresponding reflector 59 and between the anode(P-type region 53) of each PIN diode 29 and the corresponding reflector59. In addition, the reflectors 59 can be charged with staticelectricity. In this case, the electrical impact due to the reflectors59 is brought on the anodes and cathodes of the PIN diodes 29. In thiscase, by extending each reflector 59 up to under the corresponding anodeand up to under the corresponding cathode in the same manner, theelectrical impact of each reflector 59 on the corresponding anode can bemade substantially the same as the electrical impact of each reflector59 on the corresponding cathode. That is to say, the characteristics ofeach PIN diode 29 can be prevented from changing due to the staticelectricity charged in the corresponding reflector 59.

However, in the first exemplary embodiment, while each PIN diode 29 isprovided with the reflector 59, each PIN diode 30 is provided with noreflector. Therefore, the PIN diodes 29 and 30 will have differentcharacteristics. To solve this problem, in this exemplary embodiment, areflector 60 is provided under each PIN diode 30.

In FIG. 6, as with the reflector 59 provided under each PIN diode 29,the reflector 60 is formed under each PIN diode 30 and in the same layeras the gate electrodes 76 of the pixel region. Each reflector 60 isformed opposite the corresponding semiconductor layer 50 with the oxidefilm 75 therebetween.

In addition, in this exemplary embodiment, in the interlayer insulatingfilm 78 are formed contact holes 78 g and 78 h leading to the reflectors59 and 60. In each PIN diode 29, the N-type region 51 constituting thecathode is connected to the corresponding reflector 59 via thecorresponding contact holes 78 c and 78 g. In each PIN diode 30, theN-type region 54 constituting the cathode is connected to thecorresponding reflector 60 via the corresponding contact holes 78 e and78 h.

That is to say, each reflector 59 and each reflector 60 are connected tothe N-type regions 51 and 54, respectively, of the corresponding PINdiodes 29 and 30, respectively, and are out of the floating status.Therefore, the characteristics of the PIN diodes 29 and 30 can befurther stabilized.

As described above, in this exemplary embodiment, the reflector 60 isprovided under every one of the PIN diodes 30, for example, fordetecting the dark current and disposed near the PIN diodes 29 fordetecting the ambient light, and therefore each pair of PIN diodes 29and 30 can have substantially the same characteristic. In addition, thereflectors 59 and 60 are connected to the corresponding cathodes and arethereby out of the floating status. Therefore, the characteristics ofeach pair of PIN diodes 59 and 60 can be further stabilized.

Although the reflectors 59 and 60 are connected to the cathodes of thecorresponding PIN diodes 29 and 30 and are thereby out of the floatingstatus in this exemplary embodiment, all that is required is that eachreflector 59 or 60 is connected to a predetermined fixed potentialpoint. For example, the reflectors 59 and 60 may be connected to theanodes of the corresponding PIN diodes or the reference potential point.

An electronic apparatus employing any one of the above-describedelectro-optical devices is also included in the invention. FIG. 7 is aperspective view showing the configuration of a cell phone 1200employing any one of the electro-optical devices of the above-describedexemplary embodiments.

As shown in FIG. 7, the cell phone 1200 includes a plurality ofoperation buttons 1202, an ear piece 1204, a mouthpiece 1206, and theabove-described liquid crystal panel 150. All components of theelectro-optical device except for the liquid crystal panel 150 are builtinto the cell phone and are not exposed.

The electro-optical devices according to the invention can also beemployed in a projection display apparatus including a light source, alight valve modulating light emitted from the light source, and anoptical system for projecting the light modulated by the light valve. Inaddition, the electro-optical devices according to the invention canalso be employed in televisions, camcorders (viewfinders or screens),car navigation systems, pagers, electronic notebooks, calculators, wordprocessors, workstations, video-phones, POS terminals, digital stillcameras, apparatuses having a touch panel, and the like.

The electro-optical devices of the invention can be applied not only toTFT (thin film transistor) liquid crystal panels but also to liquidcrystal display panels including TFDs (thin film diodes) as switchingelements. The invention can be applied not only to liquid crystaldisplay panels but also to various electro-optical devices, for example,electroluminescence devices, organic electroluminescence devices, plasmadisplay devices, electrophoretic display devices, devices using electronemission (field emission displays, and surface-conductionelectron-emitter displays), DLP (Digital Light Processing) (also knownas DMD: Digital Micromirror Device).

The entire disclosure of Japanese Patent Application No. 2006-54425,filed Mar. 1, 2006 is expressly incorporated by reference herein.

1. An electro-optical device comprising: a display panel that includesan element substrate on which a switching element connected to a pixelelectrode is provided; a first light receiving element formed on theelement substrate and detect a luminance of an ambient light; a secondlight receiving element connected to the first light receiving elementand being shielded from an ambient light; a reflector provided downsideof the first light receiving element such that the reflector reflectsthe ambient light toward the first light receiving element.
 2. Theelectro optical device according to claim 1, the reflector beingprovided between the element substrate and the first light receivingelement.
 3. The electro optical device according to claim 2, theswitching element including a thin film transistor, and the reflectorbeing formed as the same layer with a gate electrode with the thin filmtransistor.
 4. The electro optical device according to claim 1, theswitching element, the first light receiving element and second lightreceiving element having a semiconductor layer formed as the same layer.5. The electro optical device according to claim 1, the display panelhaving an opposite substrate opposites to the element substrate, theelectro optical device further comprising: a light shielding filmprovided on the opposite substrate and defining an effective displayregion of the display panel, the light shielding film blocking theambient lights from entering the second light receiving element.
 6. Theelectro optical device according to claim 5, the light shielding filmhaving an opening, and the ambient lights incidents on the first lightreceiving element via the opening.
 7. The electro optical deviceaccording to claim 1, the display panel having an opposite substrateopposites to the element substrate, the electro optical device furthercomprising: an illuminating unit that emits lights onto the displaypanel from the element substrate side, the reflector blocking the lightsof the illuminating unit from entering the first light receivingelement.
 8. The electro optical device according to claim 7, furthercomprising a second reflector provided downside of the second lightreceiving element such that the second reflector detects the lights ofilluminating unit.
 9. The electro optical device according to claim 7,9. The electro optical device according to claim 7, further comprising asecond reflector provided downside of the second light receiving elementsuch that the second reflector blocks the lights of the illuminatingunit from entering the second light receiving element.
 10. The electrooptical device according to claim 9, the reflector and the secondreflector being formed as the same layer.
 11. An electronic apparatuscomprising the electro-optical device according to claim 1.